Preparations of Au Decahedral NCs and Segmental Ag–Au–Ag NRs

Au decahedral NCs and segmental Ag–Au–Ag NRs were prepared by following the methods reported previously.^36,37 First, a DEG solution containing AgNO₃ was prepared with a concentration of 10 mg/mL. Then, PDDA (60 μL) was mixed with 10 mL of DEG, 12.5 μL of HAuCl₄ (0.48 mol/L), and 600 μL of AgNO₃ DEG solution. The solution was well mixed at room temperature and then heated in a 210 °C oil bath. In about 15 min, the solution turned red, indicating the formation of Au decahedral NCs. After 30 min, the solution was cooled to room temperature and then 10.6 mL of water was introduced. For the synthesis of segmental Ag–Au–Ag NRs, an AgCl suspension was first prepared by mixing 5 mL of NaCl aqueous solution (2.8 mg/mL) with 5 mL of AgNO₃ aqueous solution (8 mg/mL). Then, 1.5 mL of NH₄OH was added to the AgCl suspension. The mixture immediately became transparent due to the formation of water-soluble [Ag(NH₃)₂]⁺. Then, 20 mL of Au decahedral NC solution was mixed with 700 μL of [Ag(NH₃)₂]⁺ solution. The mixtures were warmed up to 70 °C and stirred for 12 h for growing Ag–Au–Ag NRs. For purification, 1 mL of Ag–Au–Ag NR solution was mixed with 8 mL of water and then the NRs were precipitated through centrifugation. The above process was repeated three times to remove excess PDDA, DEG, and other by-products. The resulting precipitate was dispersed in 2 mL of deionized water.